Edward Markey, a Democrat from Massachusetts, asked the companies to respond to a series of questions including how they test electronic components and wireless networks to make sure that attackers cannot gain access to onboard networks. He cited recent research by security experts who uncovered cyber vulnerabilities in cars that they said hackers might be able to exploit to cause them to crash.

The letter, dated Monday, also asked about measures the carmakers take to ensure the privacy of information collected by automobile computer systems.

The Auto Alliance, an industry group whose members include those seven companies, released a statement on Tuesday saying that automakers were reviewing the letter.

“Auto engineers are incorporating security solutions into vehicles from the first stages of design and production, and their security testing never stops,” the group said in the statement. “Vehicle hardware has built-in security features that help protect safety critical systems, and auto control systems are isolated from communications-based functions like navigation and satellite radio.”

Concerns that hackers could attack cars with potentially lethal results have been growing for several years.

A group of U.S. computer scientists startled the industry in 2010 with research showing that viruses could take control of computers running car brakes, lights, locks and other systems. A year later the same researchers identified ways to remotely infect cars over Bluetooth and other wireless systems.

They kept the details of their work a closely guarded secret, declining to identify the manufacturer of the car they studied.

The National Highway Traffic Safety Administration responded by beginning an auto cybersecurity research program.

“While increased use of electronic controls and connectivity is enhancing transportation safety and efficiency, it brings a new challenge of safeguarding against potential vulnerabilities,” the agency said in a statement on Tuesday. “NHTSA recognizes these new challenges but is not aware of any consumer incidents where any vehicle control system has been hacked.”

Researchers have recently begun going public with details about vulnerabilities in automobiles in a bid to pressure manufacturers to boost security.

This past summer at the Defcon hacking conference in Las Vegas, security experts from the United States and Europe released detailed research describing cyber vulnerabilities in car models from at least three manufacturers.

The letter from Markey cited one of those presentations in his letter, a study by researchers Charlie Miller and Chris Valasek that was funded by the Pentagon’s Defense Advanced Research Projects Agency.

The two released a 100-page White Paper detailing their findings, which included ways to force a Toyota Prius to brake suddenly at 80 miles an hour (128 kph), jerk its steering wheel, or accelerate the engine. They also described a method for disabling the brakes of a Ford Escape traveling at very slow speeds, so that the car keeps moving no matter how hard the driver presses the pedal.

Markey said he believed that automakers had played down the severity of its findings.

Stuart McClure, chief executive of Cylance Inc and an expert on auto security, said that while onboard computer systems are vulnerable to hacking, they do not yet present much risk to the average driver. Such attacks are far more cumbersome to engineer than ones on PCs, he said.

But he said that the government ought to look into how automakers secure data that customers provide them when obtaining leases and loans.

“If I want to get a whole bunch of social security numbers and private data, I’m going to hack into their corporate servers and gain access to the data belonging to the millions of people who ever got a car from them,” he said.